A Soluble Fumarate Reductase in Trypanosoma brucei Procyclic Trypomastigotes

ABSTRACT. The enzyme NADH-fumarate reductase associated with the membrane fraction of Trypanosoma brucei procyclic trypomastigotes, can be solubilized by more than 50% when increasing the ionic strength to the equivalent of 150 mM KCI. The apparent K_Ms for NADH (125 μM) and fumarate (50 μM) remain close to those previously reported for the membrane-bound form of this enzyme. Other electron acceptors (i.e. oxygen or cytochrome c) appear to accept electrons in the absence of fumarate (K_M for cytochrome c = 50 μM). The drug L-092,201 (Merck, Sharp and Dohme Research Laboratories, Rahway, NJ), an inhibitor of the membrane-bound fumarate reductase, also blocked the solubilized enzyme. Given the relatively high ionic strength of the intracellular environment we propose that, in vivo, the enzyme fumarate reductase is in the mitochondrial matrix or in the soluble fraction of another intracellular compartment.     

Seventeen years of carbon dioxide enrichment of sour orange trees: final results

The long-term responses of trees to elevated CO₂ are especially crucial (1) to mitigating the rate of atmospheric CO₂ increase, (2) to determining the character of future forested natural ecosystems and their spread across the landscape, and (3) to determining the productivity of future agricultural tree crops. Therefore, a long-term CO₂-enrichment experiment on sour orange trees was started in 1987, and the final results after 17 years are reported herein. Four sour orange trees ( Citrus aurantium L.) were grown from seedling stage at 300 μmol mol⁻¹ CO₂ above ambient in open-top, clear-plastic-wall chambers at Phoenix, AZ. Four control trees were similarly grown at ambient CO₂. All trees were supplied ample water and nutrients comparable with a commercial orchard. After a peak 2–4 years into the experiment, there was a productivity plateau at about a 70% enhancement of annual fruit and incremental wood production over the last several years of the experiment. When summed over the duration of the experiment, there was an overall enhancement of 70% of total biomass production. Much of the enhancement came from greater numbers of fruits produced, with no change in fruit size. Thicker trunks and branches and more branches and roots were produced, but the root/shoot ratio was unaffected. Also, there was almost no change in the elemental composition of the biomass produced, perhaps in part due to the minimal responsiveness of root-symbiotic arbuscular mycorrhizal fungi to the treatment.     

Cladistic review of generic taxonomic characters in Xyleborina (Coleoptera: Curculionidae: Scolytinae)

Abstract A cladistic analysis of morphological characters of the subtribe Xyleborina (Curculionidae, Scolytinae) is presented. An examination of individual characters revealed little phylogenetic information in many characters currently used for delimiting genera. Phylogenetically stable characters were used for the evaluation of the contemporary generic concept. The following genera have been recovered as monophyletic: Cnestus, Dryocoetoides, Eccoptopterus, Xylosandrus, Schedlia, Sampsonius and Taurodemus. The following genera have been found to be polyphyletic: Amasa, Ambrosiodmus, Arixyleborus, Coptoborus, Coptodryas, Cryptoxyleborus, Cyclorhipidion, Euwallacea, Leptoxyleborus, Taphrodasus, Theoborus, Webbia, Xyleborinus and Xyleborus. The analysis permitted the resurrection of four genera: Anisandrus, Microperus, Pseudowebbia and Streptocranus. A number of new combinations at specific level are given: Anisandrus cornutus (Schaufuss, 1891), A. dispar (Fabricius, 1792), A. eggersi (Beeson, 1930), A. improbus (Sampson, 1913), A. longidens (Eggers, 1930), A. maiche Stark, 1936, A. obesus (LeConte, 1868), A. sayi Hopkins, 1915, A. apicalis (Blandford, 1894), A. hirtus (Hagedorn, 1904), Microperus myristicae (Schedl, 1939), M. eucalypticus (Schedl, 1938), M. huangi (Browne, 1983), M. intermedius (Eggers, 1923), M. kadoyamaensis (Murayama, 1934), Pseudowebbia armifer (Schedl, 1942), P. seriata Browne, 1963, P. squamatilis (Schedl, 1955), P. trepanicauda (Eggers, 1923), P. curvatus (Browne, 1986), Streptocranus bicolor Browne, 1949, S. bicuspis (Eggers, 1940), S. capucinulus (Schedl, 1942), S. forficatus (Schedl, 1957), S. fragilis Browne, 1949, S. longicauda Browne, 1960, S. longispinis Browne, 1986, S. mirabilis Schedl, 1939, S. usagaricus (Eggers, 1922), S. sexdentatus (Eggers, 1940). The characters most useful for generic‐level taxonomy of Xyleborina were identified and their states refined and illustrated. An accompanying illustrated multiple‐entry electronic key for the updated xyleborine classification has been published on‐line at www.scolytid.msu.edu .     

Mechanisms of resistance of freshwater macrophytes to herbivory by invasive juvenile common carp

1. Herbivory on freshwater macrophytes has been assumed to be insignificant and rare. More recent evidence suggests herbivory is common and the impact of invasive invertebrate herbivores can be substantial. However, little is known about consumption of macrophytes by fish. 2. We performed a series of feeding assays, based on the consumption by common carp (Cyprinus carpio), to determine if any mechanisms of resistance, structural or chemical, were present in five species of macrophytes (Stuckenia pectinata, Typha latifolia, Scirpus validus, Chara aspera and Ceratophyllum demersum). 3. Carp consumed more fresh whole plant tissue of C. aspera than any other macrophyte, suggesting a lack of structural or chemical deterrents. Typha latifolia, S. validus and C. demersum were consumed least as whole plants, but consumption increased when they were offered in pellet form suggesting structural defence. Crude chemical extracts from S. pectinata significantly reduced consumption of pellets by carp. Thus, plant chemistry and structure both deterred feeding by carp. 4. Experiments that focus on theory are common but their application to managing landscapes is substantially lacking. Our results provide a basis for recommending plants to be used in restoring larval habitat refugia with the aim of increasing the probability for long‐term recovery of an endangered species. Thus, this paper is an example of how experiments that tie theory to application are important for practical applications and for continued testing of theory. 5. We suggest that macrophyte–herbivore interactions play an integral part in aquatic food webs and may be as important in freshwater communities as in marine and terrestrial systems.     

In situ measurements confirm the seasonal dominance of benthic algae over phytoplankton in nearshore primary production of a large lake

1. Despite the recognition of its importance, benthic primary production is seldom reported, especially for large lakes. We measured in situ benthic net primary production by monitoring flux in dissolved inorganic carbon (DIC) concentration in benthic incubation chambers, based on continuous measurements of CO_2(aq) flux, alkalinity, and the temperature‐dependent dissociation constants of carbonic acid (K₁ and K₂). This methodology has the advantages of monitoring net primary production directly as change in carbon, maintaining continuous water recirculation, and having sufficient precision to detect change in DIC over short (i.e. 15 min) incubations, even in alkaline waters. 2. Benthic primary production on Cladophora‐dominated rocky substrata in western Lake Ontario was measured biweekly. Maximum biomass‐specific net photosynthetic rates were highest in the spring (2.39 mgC g Dry Mass^?1 h^?1), decreased to negative rates by early summer (?0.76 mgC g DM^?1 h^?1), and exhibited a regrowth in late summer (1.98 mgC g DM^?1 h^?1). 3. A Cladophora growth model (CGM), previously validated to predict Cladophora biomass accrual in Lake Ontario, successfully simulated the seasonality and magnitude of biomass‐specific primary production during the first cohort of Cladophora growth. Averaged over this growing season (May–Aug), mean areal net benthic production at the estimated depth of peak biomass (2 m) was 405 mg C m^?2 d^?1. 4. We measured planktonic primary production in proximity to the benthic study and constructed a depth‐resolved model of planktonic production. Using the CGM, benthic primary production was compared with planktonic primary production for the period May–Aug. Net benthic production from the shoreline to the 12 m contour (1–2 km offshore) equalled planktonic production. Closer to shore, benthic primary production exceeded planktonic primary production. Failure to account for benthic primary production, at least during abundant Cladophora growth, will lead to large underestimates in carbon and nutrient flows in the nearshore zone of this Great Lake.     

Estimation of bumblebee queen dispersal distances using sibship reconstruction method

Dispersal ability is a key determinant of the propensity of an organism to cope with habitat fragmentation and climate change. Here we quantify queen dispersal in two common bumblebee species in an arable landscape. Dispersal was measured by taking DNA samples from workers in the spring and summer, and from queens in the following spring, at 14 sites across a landscape. The queens captured in the spring must be full sisters of workers that were foraging in the previous year. A range of sibship reconstruction methods were compared using simulated data sets including or no genotyping errors. The program Colony gave the most accurate reconstruction and was used for our analysis of queen dispersal. Comparison of queen dispersion with worker foraging distances was used to take into account an expected low level of false identification of sister pairs which might otherwise lead to overestimates of dispersal. Our data show that Bombus pascuorum and B. lapidarius queens can disperse by at least 3 and 5 km, respectively. These estimates are consistent with inferences drawn from studies of population structuring in common and rare bumblebee species, and suggest that regular gene flow over several kilometres due to queen dispersal are likely to be sufficient to maintain genetic cohesion of ubiquitous species over large spatial scales whereas rare bumblebee species appear unable to regularly disperse over distances greater than 10 km. Our results have clear implications for conservation strategies for this important pollinator group, particularly when attempting to conserve fragmented populations.     

A single‐stranded conformational polymorphism (SSCP)‐derived quantitative variable to monitor the virulence of a Barley yellow dwarf virus‐PAV (BYDV‐PAV) isolate during adaptation to the TC14 resistant wheat line

A standardized single‐stranded conformational polymorphism (SSCP) procedure is proposed as an alternative to the time‐consuming biological characterization of Barley yellow dwarf virus‐PAV (BYDV‐PAV) isolates. Using this procedure, six of 21 overlapping regions used to scan the viral genome gave patterns specific to ‘4E’ (avirulent) or ‘4T’ (‘4E’‐derived virulent) isolates. The calibration of samples and integration of SSCP patterns corresponding to the nucleotide region 1482–2023 allowed the estimation of P_T values that reflect the proportions of a ‘4T’‐specific band. Analysis of the biological (area under the pathogen progress curve) and molecular (P_T) data suggested a positive linear relation between these variables. Moreover, sequence analysis of the nucleotide region 1482–2023 highlighted the presence of a nucleotide polymorphism (C/A₁₈₃₅) which can be considered as a candidate for virus–host interactions linked to the monitored virulence. According to these parameters, P_T values associated with ‘4E’‐ and ‘4T’‐derived populations show that: (i) long‐term infection of a BYDV‐PAV isolate on the ‘TC14’ resistant host leads to the fixation of virulent individuals in viral populations; and (ii) the introduction of susceptible hosts in successive ‘TC14’ infections results in the maintenance of low virulence of the populations. Thus, the presented study demonstrates that SSCP is a useful tool for monitoring viral populations during the host adaptation process. The described impact of host alternation provides new opportunities for the use of the ‘TC14’ resistance source in BYDV‐resistant breeding programmes. This study is part of the global effort made by the scientific community to propose sustainable alternatives to the chemical control of this viral disease.     

The distribution of breeding dippers (Cinclus cinclus (L.); Aves) in relation to stream acidity in upland Wales

SUMMARY. 1. The distribution of breeding dippers was assessed in 1984 over seventy-four sites on soft-water streams throughout mid and north Wales.
2. Sites without breeding dippers had significantly higher mean concentrations of filterable aluminium, lower mean pH, fewer trichopteran larvae and ephemeropteran nymphs, and were on rivers with more conifer afforestation on their catchments, than sites where dippers were present.
3. We speculate that influences which increase the acidity of soft-water streams could be detrimental to their populations of dippers, although further data are required on causative mechanisms.     

Lake responses to reduced nutrient loading – an analysis of contemporary long-term data from 35 case studies

1. This synthesis examines 35 long‐term (5–35 years, mean: 16 years) lake re‐oligotrophication studies. It covers lakes ranging from shallow (mean depth <5 m and/or polymictic) to deep (mean depth up to 177 m), oligotrophic to hypertrophic (summer mean total phosphorus concentration from 7.5 to 3500 μg L^?1 before loading reduction), subtropical to temperate (latitude: 28–65°), and lowland to upland (altitude: 0–481 m). Shallow north‐temperate lakes were most abundant. 2. Reduction of external total phosphorus (TP) loading resulted in lower in‐lake TP concentration, lower chlorophyll a (chl a) concentration and higher Secchi depth in most lakes. Internal loading delayed the recovery, but in most lakes a new equilibrium for TP was reached after 10–15 years, which was only marginally influenced by the hydraulic retention time of the lakes. With decreasing TP concentration, the concentration of soluble reactive phosphorus (SRP) also declined substantially. 3. Decreases (if any) in total nitrogen (TN) loading were lower than for TP in most lakes. As a result, the TN : TP ratio in lake water increased in 80% of the lakes. In lakes where the TN loading was reduced, the annual mean in‐lake TN concentration responded rapidly. Concentrations largely followed predictions derived from an empirical model developed earlier for Danish lakes, which includes external TN loading, hydraulic retention time and mean depth as explanatory variables. 4. Phytoplankton clearly responded to reduced nutrient loading, mainly reflecting declining TP concentrations. Declines in phytoplankton biomass were accompanied by shifts in community structure. In deep lakes, chrysophytes and dinophytes assumed greater importance at the expense of cyanobacteria. Diatoms, cryptophytes and chrysophytes became more dominant in shallow lakes, while no significant change was seen for cyanobacteria. 5. The observed declines in phytoplankton biomass and chl a may have been further augmented by enhanced zooplankton grazing, as indicated by increases in the zooplankton : phytoplankton biomass ratio and declines in the chl a : TP ratio at a summer mean TP concentration of <100–150 μg L^?1. This effect was strongest in shallow lakes. This implies potentially higher rates of zooplankton grazing and may be ascribed to the observed large changes in fish community structure and biomass with decreasing TP contribution. In 82% of the lakes for which data on fish are available, fish biomass declined with TP. The percentage of piscivores increased in 80% of those lakes and often a shift occurred towards dominance by fish species characteristic of less eutrophic waters. 6. Data on macrophytes were available only for a small subsample of lakes. In several of those lakes, abundance, coverage, plant volume inhabited or depth distribution of submerged macrophytes increased during oligotrophication, but in others no changes were observed despite greater water clarity. 7. Recovery of lakes after nutrient loading reduction may be confounded by concomitant environmental changes such as global warming. However, effects of global change are likely to run counter to reductions in nutrient loading rather than reinforcing re‐oligotrophication.     

Fungal community responses to precipitation

Understanding how fungal communities are affected by precipitation is an essential aspect of predicting soil functional responses to future climate change and the consequences of those responses for the soil carbon cycle. We tracked fungal abundance, fungal community composition, and soil carbon across 4 years in long‐term field manipulations of rainfall in northern California. Fungi responded directly to rainfall levels, with more abundant, diverse, and consistent communities predominating under drought conditions, and less abundant, less diverse, and more variable communities emerging during wetter periods and in rain‐addition treatments. Soil carbon storage itself did not vary with rainfall amendments, but increased decomposition rates foreshadow longer‐term losses of soil carbon under conditions of extended seasonal rainfall. The repeated recovery of fungal diversity and abundance during periodic drought events suggests that species with a wide range of environmental tolerances coexist in this community, consistent with a storage effect in soil fungi. Increased diversity during dry periods further suggests that drought stress moderates competition among fungal taxa. Based on the responses observed here, we suggest that there may be a relationship between the timescale at which soil microbial communities experience natural environmental fluctuations and their ability to respond to future environmental change.